This application relates generally to railway right-of-way maintenance equipment of the type used to repair and maintain railroad track. More specifically, the present invention relates to an apparatus for handling rail tie plates during replacement of rail ties.
Conventional railroad track consists of a plurality of spaced parallel wooden ties to which are attached a pair of spaced rail tie plates. Each tie plate is configured to rest on the upper surface of the tie and includes holes for receiving spikes or screws, as well as a canted seat or a cradle formation for receiving the bottom of the steel rail. Since two rails make up a railroad track, there are a pair of spaced tie plates on each tie. Some of the spikes are used to secure the tie plate on the tie and others are used to secure the base of the rail to the tie plate cradle.
During track maintenance operations, it is common to periodically remove worn out or rotten ties. This is accomplished by first removing the spikes which hold the plates to the tie as well as to the rail. Next, a machine, such as disclosed in commonly-assigned U.S. Pat. No. 6,463,858 which is incorporated by reference, lifts the rail and extracts the worn tie from underneath. As the tie is extracted, the loosened tie plates either fall into the rail bed or ballast, or are retained on the removed tie. Conventional practice is to manually remove the plates and throw them off to the side of the ballast so that they do not interfere with the replacement of the new tie. Once the new tie is inserted under the raised track, the plates must be reinserted in the appropriate position to support the rail and for re-spiking.
To avoid on the job injuries, especially those involved with handling tie plates, which typically weigh approximately 18-40 pounds and are heavy to manipulate, railways have attempted to mechanize the tie replacement and plate placement process as much as possible. One attempt has been to provide a mechanism which grips the plates and secures them to the rail as the tie is removed from beneath the plates. This system has not been widely accepted by the railroads because of its relatively complicated mechanism, and because in many instances the insertion of the new tie will cause particles of railway ballast to be retained on top of the tie and interfere with the repositioning of the tie plates. These conventional mechanisms have no way to remove unwanted ballast particles from the top surface of the tie.
Another drawback of conventional mechanized plate placement devices is that their speed is relatively slow and they cannot keep up with the other operations of the rail maintenance gang. Using manual removal and placement of tie plates, the tie replacement process typically operates at a rate of about 15 ties per minute. Conventional mechanized plate removal devices operate in the range of 3 to 5 ties per minute. At this point, this rate of production is unacceptable to the railroads.
Commonly-assigned U.S. Pat. No. 6,863,717 discloses a rail plate handling device that is designed for use in conjunction with the tie extraction and replacement machine disclosed in U.S. Pat. No. 6,463,858 discussed above. In operation, the plate handling device uses a pair of powered jaws to grasp the tie plate prior to tie extraction, and retract the plate away from the tie as it is extracted, then the jaws are released to drop the plate upon the rail ballast between the rails. The plates are then manually collected and repositioned for replacement of the ties. The device of the '717 patent was not commercially adopted due to operational speed constraints.
Thus, there is still a need for an improved rail plate handling device that decreases or eliminates manual handling of rail tie plates during the tie extraction and replacement process.